How important is MTBF?

Hi there just preoreder supercharged edition a few days ago and I'm loving it!
My question is how important is MTBF, and what should the range be for different types of engines.
My most of my non turbo engines have an MTBF of 42-48k
My turbo engines have 36-43k
And my non turbo performance V8 has 30k
Are these ok? And what is the best way to increase MTBF without losing a lot of performance
My question is how important is MTBF, and what should the range be for different types of engines.
My most of my non turbo engines have an MTBF of 42-48k
My turbo engines have 36-43k
And my non turbo performance V8 has 30k
Are these ok? And what is the best way to increase MTBF without losing a lot of performance